JDK1.8快速入门

函数式接口

Arrays.sort(words, (first, second) -> Integer.compare(first.length(), second.length())); BiFunction<String, String, Integer> comp = (first, second) -> Integer.compare(first.length(), second.length()); 常见的函数式接口(推荐使用)，和C#Action<T>,Function<T, R>类似 Runnable,Supplier<T>,Consumer<T>， Function<T, R>, Predicate<T>

方法引用

Arrays.sort(words, String::compareToIgnoreCase);

构造器引用

list.stream().collect(Collectors.toList());

默认方法，接口中的静态方法

不太推荐

概念

所有的lambda表达式都符合闭包，且是延迟执行的

创建Stream

Stream<String> song = Stream.of("Shanghai", "Beijing");

filter,map,flatmap方法

分别对应C#中Linq的where,select和selectMany   Optional<TravelTicket> tempTT = availableTicketMapper.values().stream().flatMap(i -> i.stream()) .filter(i -> i.getID() == item.getTravelMoneyID()).findFirst()

常见操作

去除重复: .distince() 排序.sorted(), 反向.reversed()   List<TravelTicketCommonDTO> targetList = orderedAvailableTTInfoList.stream() .filter(i -> i.getTicketCategoryID().equals(item.getTicketCategoryID()) && i.getCanRefundAmount().compareTo(BigDecimal.ZERO) > 0) .sorted(Comparator.comparing(TravelTicketCommonDTO::getExpirationDate).reversed()) .collect(Collectors.toList()); 聚合方法 .max(), findFirst(), .findAny(), .anyMatch() 聚合操作 .reduce((x,y)->x+y)，reduce(BigDecimal.ZERO, BigDecimal::add) 分组和分片: .groupingBy(), mapping(), joining() 并行流: .parallel()

Optional类型

Optional<T>是对T类型封装，它不会返回null，使得引用更安全

时间线Instant

Instant start = Instant.now(); Thread.sleep(1000); Instant end = Instant.now(); Duration timeElapsed = Duration.between(start, end); long millis = timeElapsed.toMillis();

本地日期LocalDate

LocalDate today = LocalDate.now(); LocalDate oneDay = LocalDate.of(2017, 7, 9); LocalDate addDay = LocalDate.now().plusDays(10);

日期校正器TemporalAdjueters

获取2017年5月的第一个周二 LocalDate time = LocalDate.of(2017, 5, 1) .with(TemporalAdjusters.nextOrSame(DayOfWeek.TUESDAY));

本地时间LocalTime

LocalTime time = LocalTime.of(16, 37, 11);

带时区的时间ZonedDateTime

ZonedDateTime applloTime = ZonedDateTime.of(2017, 5, 9, 16, 40, 11, 0, ZoneId.of("America/New_York"));

格式化和解析DateTimeFormatter

用于替代过去的DateFormat,SimpleDateFormat

遗留代码的互操作

Instant start = Instant.now();其他类型的操作类似 Date oldDate = Date.from(start);

原子值

AtomicLong nextNumber = new AtomicLong(); nextNumber.incrementAndGet();

ConcurrentHashMap的改进

ConcurrentMap<String, Integer> map = new ConcurrentHashMap(); map.putIfAbsent("age", 100); map.compute("name", (k, v) -> v == null ? 1 : v + 1); map.merge("age", 1, (oldValue, newValue) -> oldValue + newValue); 批量数据操作：reduceValue, reduceKeys

并行数组操作

String[] people = new String[]{"xionger", "shuaishuaida"}; Arrays.parallelSort(people);

Future，和.NET的Task<T>类似

CompletableFuture<String> contents = CompletableFuture.supplyAsync(() -> getAsync()); 这部分知识之后再加强

字符串

String joined = String.join("/", "user", "local", "bin");

数字扩展

Long testValue = Integer.toUnsignedLong(Integer.MAX_VALUE);

新的数值函数

int result = Math.floorMod(Math.toIntExact(100L), 3);

新增集合方法

list.forEach((item) -> System.out.println(item)); Map: remove, putIfAbsent, computeIf, merge 排序：Arrays.sort(people, Comparator.comparing(Person::getAge));

使用文件

这儿看到try-with-resource，等价于using,java代码也可以和.net一样简介 try (Stream<String> lines = Files.lines(path)) {     Optional<String> pwd = lines.filter(s -> s.contains("pwd")).findFirst();}

Base64编码

Base64.Encoder encoder = Base64.getMimeEncoder(); try (OutputStream output = Files.newOutputStream(encoderPath)) {     Files.copy(originalPath, encoder.wrap(output));}

注解

通过在注解上添加@Repeatable，使得注解可多次使用 可以使用基于类型的注解 private @NonNull List<String> names = new ArrayList<>(); 方法参数反射，可以反射获取参数的名称

Java7

使用Path接口来代替File类 Path absolute = Paths.get("/", "home", "shanghai "); Files.write(absolute, content.getBytes(StandardCharsets.UTF_8));